The invention relates broadly to a tool useful for shifting a sleeve positioned slideably inside of a tubular member, such as a well casing. In a specific application, the tool is designed for shifting a slidable sleeve inside of a port collar, of the type used in well cementing operations.
When boreholes are drilled to recover oil or gas, a well casing is lowered into the hole and cemented, usually at the lower end of the hole and frequently at other locations above the lower end. When the lower end of the casing is cemented, usually referred to as primary cementing, a cement slurry is passed down through the casing and up into the annular space defined between the casing and the borehole. Cementing above the lower end of the borehole is usually done later than the primary cementing job, that is, during the productive life of the well. The later operations are sometimes referred to as secondary cementing, or stage cementing.
One of the devices commonly used in stage cementing operations is a port collar. A port collar can be generally described as a coupling between sections of well casing which has openings (ports) in the collar wall. Positioned inside the collar is a sliding sleeve, referred to as a port collar sleeve, which also has ports in the sleeve wall. Prior to cementing the sleeve is in a position such that it closes off the collar ports. When it is desired to pump cement into the borehole annulus through the openings in the port collar, a shifting tool is used to slide the sleeve to a position in which the sleeve ports and collar ports are in direct alignment.
Some of the known shifting tools are described in U.S. Pat. Nos. 2,667,926 (Alexander), 3,768,562 (Baker), and 3,948,322 (Baker). In general, the shifting tools described in these references require a mechanical operation which gives the tool several disadvantages. For example, the mechanical linkage of the tool can sometimes "hang up" inside the port collar-sleeve assembly. When this happens, it makes it difficult to disengage the tool between each shifting sequence. Another problem is that some of the tools are designed to engage and shift only one port collar at a time, that is, the engaging mechanism is not capable of being retracted to enable the tool to pass through one port collar to engage another. Another undesirable feature is that some of the tools require rotating the drill pipe to which the tool is fastened to latch the tool into the port collar sleeve.
The shifting tool of this invention overcomes the problems mentioned above, by providing an engaging mechanism which operates by hydraulic fluid pressure, rather than by mechanical linkage. The tool described herein is also simpler to operate than the prior tools because of fewer moving parts. In addition, this tool can pass through any number of port collars in a given drill string. This feature enables the tool to engage and shift each port collar sleeve an indefinite number of times in a given operation.